EPITAXIAL SILICON GROWTH-CONDITIONS AND KINETICS IN LOW-TEMPERATURE ARF EXCIMER LASER PHOTOCHEMICAL-VAPOR DEPOSITION FROM DISILANE

Homoepitaxial Si films were deposited using an ArF excimer laser beam parallel to the substrate to photodissociate Si2H6 at low temperatures (250-350-degrees-C) under laser intensity and Si2H6 partial pressure conditions that result in low initial photofragment concentrations (< 10(13) cm-3). Total pressure and flow conditions were chosen such that there is little secondary photolysis of the initial photofragments. The deposition yield of solid Si from photoexcited Si2H6 is estimated to be 0.20+/-0.04, indicating that in order for film growth to result solely from the primary products in ArF laser (193 nm) photolysis of Si2H6, a sticking coefficient greater-than-or-equal-to 0.6 must be assigned to the dominant growth precursor. Growth rates vary linearly with laser intensity and Si2H6 partial pressure over a range of 1-15 mJ/cm2 pulse and 5-40 mTorr, respectively. Increasing the distance between the laser-beam axis and the silicon substrate results in a reduction of the growth rate that can be explained by gas-phase chemical reaction of the growth precursors as they diffuse to the substrate. Epitaxy is maintained for temperatures above the threshold for thermal decomposition of surface (SiH2)n chains at approximately 250-degrees-C, and for temperatures below the onset Of Si2H6 pyrolysis and rapid thermal desorption of surface H-2 at approximately 350-degrees-C.